Numerous examples of spaces which disturb the propagation of acoustic waves are known. Among other examples there may be mentioned:
railway stations and air terminals, or more generally public places in which multiple reflections of sound waves make it difficult to understand the broadcast sound messages intended for users, PA1 and the spaces in which multi-scattering media would be arranged at least locally, that is to say media in which are dispersed or distributed elements which reflect or individually scatter the acoustic waves, with weak absorption, of a nature such as to cause a spreading of at least one order of magnitude of the duration of an acoustic pulse. PA1 where: PA1 h.sub.ij (-t) represents the temporal inversion of the impulse response h.sub.ij (t), previously determined and stored, between loudspeaker i and a predetermined so-called "calibration" point j belonging to the target zone, the target zone comprising a number p of calibration points, p being a natural integer at least equal to 1, the impulse response h.sub.ij (t) corresponding to the acoustic signal received at the point j when loudspeaker i emits a short acoustic pulse, PA1 the weighting coefficients a.sub.j are all equal to 1; PA1 the subset of active loudspeakers comprises all the loudspeakers of the space to be sound-swept; PA1 the number p of calibration points of the target zone is at least equal to 2; PA1 the number n of loudspeakers is at least equal to 2; PA1 the signal S(t) corresponds at least in part to a sound signal chosen from among the signals representative of the human voice and the signals representative of musical snatches; PA1 the space to be sound-swept is a place which receives the public, and the signals S(t) correspond at least in part to public information messages; PA1 in the course of at least certain of the soundsweeping steps, a number q of target zones is simultaneously sound-swept, where q is a natural integer at least equal to 2, each active loudspeaker i then emitting the superposition of q acoustic signals ##EQU2## PA1 where k is a natural integer lying between 1 and q corresponding to each target zone, S.sub.k (t) representing the information-carrying acoustic signal intended to be broadcast in the target zone of index k: use is thus made of the above-mentioned property of the process according to the invention, according to which each signal S.sub.k (t) is perfectly received in the target zone k, but very poorly received, or not received at all, in the other target zones; PA1 the target zone considered in at least certain of the sound-sweeping steps is as restricted a zone as possible comprising at least one calibration point and in which there is at least one person who is the destination of a voice message represented by the signal S(t). PA1 a number n of loudspeakers distributed inside the said space, n being a natural integer at least equal to 1, PA1 at least one input pathway for receiving a signal S(t) carrying information to be transmitted in the form of acoustic waves in at least one zone, termed the target zone, which belongs to the space to be sound-swept, this transmission being carried out by having acoustic signals s.sub.i (t) emitted by at least one subset of so-called active loudspeakers, which subset includes at least one loudspeaker chosen from among the n above-mentioned loudspeakers, PA1 a signal processing system for determining each signal s.sub.i.sup.h (t) via the formula: ##EQU3## PA1 where PA1 a) the emission is effected, from the location where it is desired to concentrate the energy, of a short acoustic pulse, having a first duration, PA1 b) the acoustic signals coming from the said location through a multi-scattering medium are gathered on a network of transducers and are recorded, for a second duration which is greater by at least one order of magnitude than the first duration; and PA1 c) return signals derived from signals gathered by temporal inversion and amplification are emitted toward the multi-scattering medium, from the said transducers. PA1 means for causing the emission of a brief acoustic pulse from the said location; PA1 a network of transducers; PA1 a multi-scattering medium intended to be interposed between the network of transducers and the said location, and devised so as to temporally spread the said acoustic pulse in such a way as to increase its duration by at least one order of magnitude at the level of the network of transducers, PA1 the network of transducers being controlled so as to emit acoustic signals obtained by temporal inversion and amplification of acoustic signals picked up in response to the emission of the said pulse.
The objective of the present invention is in particular to optimize the transmission of information inside such a space.